The present invention relates to a polarizing plate and a liquid crystal display apparatus using the same, particularly to a liquid crystal display apparatus of transverse electric field switch mode.
In response to an increasing level of performance and definition of the liquid crystal display apparatus, a polarizing plate protective film used in the polarizing plate is required to meet various requirements.
A film made of cellulose ester is employed as a polarizing plate protective film of commonly used liquid crystal display apparatus. To manufacture the cellulose ester film, a solution casting method is generally utilized in order to ensure flatness. The refractive index along the thickness tends to reduce relative to the refractive index of the film inner surface.
Patent Document 1 describes the cellulose ester film whose optical anisotropy is reduced by addition of an ethylenic polymer. The film with reduced Rt has been found out to easily cause deterioration of the polarizer after a long-term use.
The polarizing plate is required to provide excellent characteristics in dimensional stability and retardation stability subsequent to a long-term use or exposure to high temperature or high humidity since it has a serious impact on the display performance (viewing angle, tint and gradation) of the liquid crystal display. In particular, the polarizing plate is required to have superb dimensional stability in the direction of the absorption axis of the polarizer, and prominent resistance to deterioration of the polarizer
If there is much dimensional variation of the polarizing plate subsequent to a long-term use or exposure to high temperature or high humidity, stress will occur between the polarizing plate and agglutinant or liquid crystal cell bonded through the agglutinating layer, a so-called light leakage occurs wherein a white patch will occur at the time of black display
It has been found in particular that a phenomenon such as the aforementioned light leakage, reduction in contrast and variations in visibility such as color shift occur to the liquid crystal display apparatus of transverse electric field switching mode (hereinafter referred to as “IPS type”) due to generation of a vast amount of heat from the backlight, when the polarizing plate containing a cellulose ester film with the reduced optical anisotropy as mentioned above is utilized, or the liquid crystal display apparatus has been subjected to a long-term use or adjustment of the screen brightness. This has required prompt action to be taken for improvement.
[Patent Document 1] Japanese Non-Examined Patent Publication 2003-12859